By Sarah Cooper, Technical Reviewer, MCS Certified Heat Pump Engineer · Last reviewed
Heat Pump: New Build vs Retrofit in the UK (2026)
Updated July 2026
TL;DR
- A heat pump in a new build starts from a clean slate, so it can be sized for a low flow temperature, big radiators or underfloor heating, and airtight fabric from day one.
- A heat pump in a retrofit has to work with the home you already have, which usually means a heat loss survey, some radiator upgrades, and a plan to lower flow temperature.
- The biggest financial gap is grants. Retrofit projects can claim the £7,500 Boiler Upgrade Scheme grant. New builds generally cannot, because the scheme excludes new construction.
- Running costs come down to the same thing in both cases: fabric quality and flow temperature, not the badge on the outdoor unit.
- If you are buying a new build, ask for the heat loss calculation and the design flow temperature. If you are retrofitting, book a proper survey before you accept any quote.
Heat pumps behave the same way whether they sit outside a brand new house or a Victorian terrace. The physics does not change. What changes is everything around the pump: the insulation, the pipework, the radiators, and the money on the table. Those differences decide how well the system runs and how much you pay to run it.
This guide compares the two routes for UK homeowners in 2026. It covers the design decisions, the grant rules, realistic costs, and the practical checks you should make before you sign anything. Sarah Cooper, an MCS certified engineer, wrote it from the perspective of someone who commissions both types of system.
What is the difference between a new build and a retrofit heat pump?
A new build heat pump is designed into the house before it is built, while a retrofit heat pump is added to a home that was designed around a gas boiler. That single fact drives almost every other difference you will read about below.
In a new build, the heating engineer works alongside the architect. Radiator sizes, pipe runs, cylinder location, and the design flow temperature are all chosen together. The fabric is built to current Building Regulations, so heat loss is low and the pump can run gently and efficiently.
In a retrofit, the heat pump has to fit a home that already exists. The walls, windows, radiators, and pipe diameters are fixed points you have to work around. Some of them are fine as they are. Others need upgrading before the pump can hit its efficiency target. A full heat loss survey is the tool that tells you which is which.
Neither route is better in the abstract. A well designed retrofit in a solid, insulated home can outperform a rushed new build with undersized emitters. The quality of the design matters more than the age of the house.
Do new builds have to use heat pumps in 2026?
New builds do not yet have a blanket heat pump mandate in 2026, but the direction of travel is fixed and gas boilers are being phased out of new homes. The Future Homes Standard is the policy that closes the door on fossil heating in new construction.
The government set out this direction in the Future Homes and Buildings Standards consultation, which targets a large cut in carbon emissions from new homes compared with older regulations. In practice, that level of emissions reduction is very hard to reach with a gas boiler, so most developers are moving to heat pumps as the default heating system.
If you are buying a new build in 2026, you may still find some plots with gas, some with heat pumps, and a growing number of all electric homes with solar and battery storage. The important point for you as a buyer is not the label. It is whether the system was designed properly. Our developer focused new build guide explains what a compliant design should include.
For retrofits, there is no requirement to switch. You can keep a working gas boiler. The reason people move is running cost, comfort, and the grant, not a legal deadline.
Which route gets the grant?
Retrofit projects can claim the £7,500 Boiler Upgrade Scheme grant, while new builds are generally excluded from it. This is the single largest financial difference between the two routes.
The Boiler Upgrade Scheme pays £7,500 towards an air source heat pump, and the grant is deducted by your installer before you pay. The official scheme eligibility rules state that the property must be replacing an existing fossil fuel heating system, which is why new builds do not usually qualify. Uptake has grown steadily, and the government publishes the numbers in its Boiler Upgrade Scheme statistics.
The effect on cost is large. A retrofit air source heat pump that costs £11,000 to fit becomes £3,500 after the grant. A new build heat pump has no grant to offset it, but the cost is usually rolled into the mortgage as part of the house price, so you never see a separate bill. You pay for it, just spread across 25 or 30 years.
There are two practical eligibility points for retrofits worth remembering:
- You need a valid EPC without outstanding recommendations for loft or cavity wall insulation. Our EPC requirements guide covers the detail.
- The installer must be MCS certified, and they apply for the grant on your behalf.
How do design differences affect running costs?
Running cost is governed by the flow temperature the system needs, and new builds have a natural head start because they are built to run cool. A retrofit can reach the same low flow temperature, but it often needs some upgrades to get there.
Flow temperature is the temperature of the water the pump sends to your radiators or underfloor loops. The lower it is, the more efficiently the pump runs. A pump running at 35 degrees is far cheaper to run than the same pump forced up to 55 degrees to heat undersized radiators. Our flow temperature guide explains why this single number drives your bills.
Here is how the two routes typically compare on the factors that set flow temperature:
| Factor | New build | Retrofit |
|---|---|---|
| Fabric and airtightness | High, built to current regs | Variable, may need insulation work |
| Emitter sizing | Sized for low flow temperature | Often needs larger radiators |
| Underfloor heating | Common, easy to install | Possible but disruptive |
| Typical design flow temp | 35 to 40 degrees | 45 to 55 degrees before upgrades |
| Pipework | New, correct diameter | May need some replacement |
The gap is real but not permanent. A retrofit that upgrades a handful of key radiators and improves loft insulation can hit new build efficiency levels. The work is where the cost and disruption sit.
Radiators and emitters
New builds fit oversized radiators or underfloor heating from the start, while retrofits usually keep most existing radiators and upsize only the ones that fall short. You rarely need to replace every radiator in a retrofit, which surprises many homeowners.
A heat loss calculation for each room tells the installer which radiators are large enough for the lower flow temperature and which are not. Often it is two or three radiators in the coldest rooms that need upgrading. Our heat pumps and radiators guide explains how the sizing works and what to expect. Where floors are being lifted anyway, underfloor heating is the ideal partner for a heat pump because it runs at the lowest flow temperatures of all.
What does each route cost in 2026?
A retrofit air source heat pump typically costs £8,000 to £14,000 before the grant, while a new build heat pump is bundled into the purchase price and rarely appears as a separate figure. The headline numbers look different, but the underlying hardware is similar.
For a retrofit, the price depends on the size of the home, the number of radiators that need upgrading, and whether the cylinder location is straightforward. Our installation cost breakdown itemises where the money goes. After the £7,500 grant, most homeowners pay between £1,500 and £6,500 out of pocket.
For a new build, the heat pump is part of the specification. The developer pays trade prices, installs during construction when access is easy, and passes the cost to you inside the house price. You do not get a grant, but you also avoid the disruption, the survey, and the radiator upgrades because everything is sized correctly from the start.
A rough comparison for a typical three bedroom home:
| Cost item | New build | Retrofit |
|---|---|---|
| Heat pump and cylinder | In house price | £8,000 to £14,000 |
| Radiator or emitter upgrades | None, sized new | £0 to £2,500 |
| Grant applied | None | Minus £7,500 |
| Typical net cost to you | Hidden in mortgage | £1,500 to £6,500 |
If you want to model your own home, the heat pump calculator gives a quick estimate based on your property.
Which is more efficient in real use?
New builds tend to record slightly higher real world efficiency because they are airtight and designed for low flow temperatures, but a good retrofit closes most of the gap. The deciding factor is the quality of the install, not the age of the building.
The metric to watch is the seasonal performance factor, which measures how many units of heat you get for each unit of electricity across a full year. A well commissioned system in a well insulated home, new or old, should comfortably beat a gas boiler on carbon and often on cost. A poorly commissioned system in either type of home will disappoint.
This is why the survey and commissioning matter more than the brand. Ask any installer for the design flow temperature and the predicted performance figure before you commit. If they cannot give you those numbers, keep looking. For a wider view of whether the switch stacks up for your situation, our guide on whether a heat pump suits a three bedroom semi works through a common case.
What does the retrofit process actually involve?
A retrofit runs through survey, design, installation, and commissioning, and the whole job usually takes one to three days on site once the survey is done. A new build skips the survey stage because the design is fixed during construction.
For a retrofit, the sequence looks like this:
- Heat loss survey. An MCS installer measures each room and calculates how much heat it loses on a cold day. This is the single most important step, because it sets the flow temperature and tells you which radiators need upsizing.
- System design. The installer selects the pump size, cylinder, and any radiator changes, then produces the paperwork the grant requires.
- Installation. The old boiler comes out, the pump goes in outside, the cylinder is fitted, and any radiator swaps are done. Most homes are without heat for part of a day, not for the whole job.
- Commissioning. The installer balances the system, sets the weather compensation curve, and shows you how the controls work. Poor commissioning is the most common reason a good system underperforms.
New builds compress all of this. The design happens at the drawing board, the pump is installed while the house is being built, and commissioning is part of the developer handover. That is why a new build heat pump is far less disruptive to the buyer. There is no survey to book, no dust, and no cold week waiting for radiators.
The trade off is control. In a retrofit you choose the installer, review the design, and can push for a lower flow temperature or a better cylinder. In a new build you inherit the developer's choices, so the questions you ask before you exchange contracts matter a great deal.
Are the planning and noise rules different?
The planning and noise rules are the same technology rules for both routes, but new builds clear them at the design stage while retrofits have to check them against an existing plot. In England, an air source heat pump is usually permitted development if it meets siting and noise conditions.
For a retrofit, the outdoor unit has to sit within permitted development limits or you need a planning application. The main conditions are that the unit is not too close to a boundary, does not sit forward of the front wall on a road facing elevation, and stays under the noise threshold measured at the neighbour's window. Homes in conservation areas, flats, and listed buildings face tighter rules, so those cases need a closer look.
New builds handle all of this before a single brick is laid. The heat pump location is chosen on the plan, noise is modelled, and the whole scheme is signed off through building control. As a buyer you inherit a compliant installation, which is one of the quiet advantages of the new build route.
Scotland and Wales apply their own permitted development rules, and they differ from England in the detail. Whichever nation you are in, a competent MCS installer will confirm the position before quoting, and for a new build the developer carries that responsibility.
Frequently asked questions
Can I get the £7,500 grant on a new build?
No. The Boiler Upgrade Scheme is for replacing an existing fossil fuel heating system, so new builds are generally excluded. The scheme rules on gov.uk set out the eligibility conditions. New build heat pump costs are usually included in the purchase price instead.
Is a retrofit heat pump as efficient as one in a new build?
It can be, if the home is insulated to a reasonable standard and the emitters are sized for a low flow temperature. New builds have an advantage on airtightness, but a good retrofit with a couple of upgraded radiators and topped up insulation reaches similar performance in practice.
Do I need to replace all my radiators for a retrofit?
Usually not. A heat loss survey checks each room, and typically only the radiators in the coldest rooms need upsizing. Many retrofits keep most of the existing radiators unchanged, which keeps cost and disruption down.
Will new builds be forced to have heat pumps?
New builds are not required to fit a specific technology in 2026, but the Future Homes Standard sets emissions targets that gas boilers struggle to meet. Most developers are choosing heat pumps as the default because they are the easiest way to comply.
The bottom line
The choice between new build and retrofit is rarely a choice at all. If you are buying a new home, the heating system is part of the package, and your job is to check that it was designed and commissioned properly. If you already own your home, retrofit is the route, and the £7,500 grant makes it far more affordable than the sticker price suggests.
In both cases, the same two things decide whether you end up happy: the fabric of the building and the flow temperature the system runs at. Get those right and a heat pump will be cheaper and cleaner than the gas boiler it replaces. Get them wrong and no amount of brand loyalty will save the bills.
Start with a proper survey if you are retrofitting, or ask for the heat loss calculation if you are buying new. The paperwork is boring, but it is the difference between a system that works and one that does not.